The present invention relates to a process and a device for determining the driving torque of a vehicle when it starts. In addition, it also relates to a process and a device for determining externally generated variables that drive or brake a vehicle as well as for supporting uphill starting.
Generally when a vehicle begins moving the operating conditions of the engine, amongst other things, change in so far as the motor changes from an idle state (in this application idle does not necessarily refer to the idling speed of the motor, but always to the operation of the motor without the vehicle as a load) to normal running (loaded operation) where the motor propels the vehicle, so that the motor output is used to a large extent in the manner defined to drive the vehicle. The transient state is controlled by means of the clutch in the manual transmissions. In automatic transmissions the change of states is controlled by the torque converter. However, in all cases it is difficult to determine the torque available for the actual driving torque during the transition. Thus, it is not exactly known which part of the engine torque is available for propelling the vehicle. In many applications this has proven disadvantageous, for example in connection with auxiliary support units for uphill starting. When a vehicle has to initiate movement uphill, the downgrade force acts as a rearward-driving torque at first, whereas the braking force and engine torque act as a stopping or forward-driving force. When an auxiliary support unit for uphill starting is to be provided, it must be ensured, amongst other things, that the vehicle does not roll backwards under any circumstances. Despite the fact that the engine is in the above-mentioned transient state, all forward-driving and rearward-driving influences have to be known, so that suitable control elements, for example a remotely controllable vehicle driving brake (e.g. an analog remotely controllable vacuum brake-force booster) and/or a remotely controllable parking brake (e.g. an electric parking brake), can be influenced in an appropriate manner.
Furthermore, the present invention relates to a process and a device for determining an externally generated variable that drives or brakes a vehicle and in particular such a torque. The longitudinal dynamics of a vehiclexe2x80x94speed and accelerationxe2x80x94are influenced by different internal and external variables, in particular torques. Internal variables/torques according to this description, for example, are the engine torque, braking torque or road resistance (that can be described internally, for example, on the basis of tables based on values gained by experience or through constant values or equations which take into consideration the vehicle motion state with the characteristics/parameters of the vehicle). These variables can be determined comparatively accurately by means of various measures, so that their influence on the longitudinal dynamics can be taken into account. Furthermore, there are also externally generated variables which arise in particularly variable forms in addition to the above-mentioned (internally describable) road resistance. This includes, for example, the downgrade force when a vehicle is driving on a sloped roadway. The downgrade force gives rise to a torque that affects the longitudinal dynamics of the vehicle. The same is true, for example, in connection with windforce, extraordinary rolling resistance or similar forces. These externally generated variables either cannot be determined at all or only with great difficulties by means of customary sensors. This invention renders unnecessary any sensor technology generally required for this purpose.
The present invention discloses a process and a device for determining the driving torque of a vehicle as it is starting.
Furthermore, the present invention discloses a process and a device for determining externally caused variables that drive or brake a vehicle, in particular such a torque.
Still further, the present invention discloses a process and a device to support uphill starting.
The driving torque of a vehicle as it is starting is obtained by determining the idling properties of the engine on the basis of a model and comparing meaningful output values of this model to actually measured corresponding values (observer principle). The difference between the values of the model and the actually measured variables can be traced back to the fact that the engine does not run completely unloaded in the transient state from no-load running to loaded running, but gives off a part of its power to the vehicle (already) during the transient state. The driving torque of the vehicle effective during the transient state can be inferred by evaluating a variable of the model and the measured variable. In this connection, please refer once more to the definition of xe2x80x9cidle statexe2x80x9d provided above.
The variables generated externally and, in particular, torques are determined by another observer. This observer receives variables generated internally that drive or brake a vehicle, in particular torques. On the basis of these it determines the possible development of the longitudinal dynamics of a vehicle, compares this result with the actually measured values of the longitudinal dynamics and infers externally generated variables that drive or brake a vehicle, in particular torques, from any deviations.
Knowledge of externally generated variables that drive or brake a vehicle, in particular such torques, is desirable for various applications. One example of such an application is a support device for uphill starting. Support devices for uphill starting are designed to simplify the complicated handling of brake, parking brake, clutch and engine when a vehicle starts uphill. At the same time, however, it must be ensured that the vehicle does not roll backwards under any circumstances, for example to avoid colliding with any vehicles behind it. When a vehicle is to start uphill, the laws diagrammatically shown in FIG. 10 apply as an initial approximation. The weight force FG of the vehicle can be reduced to a normal component FN and a tangential component FT at the tire of a one-wheel model. Together with the tire radius rR FT results in a downforce torque MH according to the following equation:
xe2x80x83MH=FGxc2x7sin xcex1xc2x7rR.
For this purpose, xcex1 is the angle of gradient. Without any additional influences, the downforce torque MH would cause the vehicle to roll downhill. It is counter-acted by the braking torque. MB that stops the vehicle and the engine torque MM that is additionally introduced during starting. A support device for uphill starting, for example, may have an influence on the braking torque MB. This influence must be such, however, that it is always ensured that the inequality
MH less than MB+MM
is fulfilled. Only then can it be definitely ensured that the vehicle does not roll backwards. In order to fulfill the above equation, the downforce torque must be known.
Similar considerations as those described above apply in dynamic situations (vehicle speed is not equal to zero). When a vehicle moves uphill slowly in city traffic, for example, considerations as those described above may become important. In such situations it would be desirable to know the externally generated variables that drive or brake a vehicle, in particular such torques, so as to be able to influence the vehicle suitably.